On Tue, 15 Feb 2005, Steven M. Schultz wrote: > On Tue, 15 Feb 2005, Trent Piepho wrote: > > > There is no need to do anything special for 720x480 instead of 704x480, you > > can use the same math. > > What about the difference in SAR between D1 and DV/DVD? If it's not
D1, DVD, and DV all use a sampling rate of 13.5 MHz and have the same sample aspect ratio. I have no idea where 9:10 would come from, expect as some sort of compromise value, like the MPEG1 list of SARs. > Pick up a book on FCP-HD or Adobe's "Premiere" (Photoshop even has > a NTSC DV preset that uses 9:10 and 720x534). If you want 720x486 output, you would use 720x534 input. From the simple formula I posted before: Output Height = Input Height / Input SAR * Output SAR Output Height = 534 / (1/1) * (10/11) = 485.45 Think of the relation like this: 720x486 (10:11) <=> 720x534 (1:1) Read as, "720 by 486 with a sample aspect ratio of 10 to 11 is equivalent to 720 by 534 with a sample aspect ratio of 1 to 1." > > If you are going from a non-anamorphic DVD to a computer, the input SAR is > > He's going, as I recall from computer to DVD so it'd be from 1:1 to > non-square. I suppose when I used "input" and "output" it confused things. You are just finding what resolution and SAR is equivalent to another resolution and SAR, it doesn't matter which direction you are going. > What does seem to be confusing me (perhaps others too) is that there > is the SAR of 10:11 (ratio of 12.272727 and 13.5MHz) and the > "NTSC DV" SAR of 9:10 which is used by some fairly highend video > editors. Sounds like they are just approximating 10/11 = 0.9090909090... to 0.9? > > If you are going from a non-anamorphic DVD to a computer, the input SAR is > > 10/11, and the output is 1/1. The input height is 480 and the input width > > is > > Or 9/10 depending which book was last consulted :) Can you find anything on the web that defines D1/DVD/DV as having a 9/10 SAR? > I'm not sure if fiddling with the numbers (if I put 720x528 in I can > get 720x480 out) instead of padding 704 to 720 is the right thing to > do. If you think about it, it's not different at all. Start with 720x528 and scale to 720x480 or start with 704x528, pad 8 pixels on each side to get 720x528, and then scale to 720x480. The only difference is do you want the 8 pixel border to be black or do you want to stick something there? > > Want to scale vertically and get 720x480? > > 480 / (10/11) * (1/1) = 528, use 720x528 > > > Want to scale vertically and get 704x480? > > 480 / (10/11) * (1/1) = 528, use 704x528 > > Huh? The same vertical size being used? That's making the assumption > that the 720x480 image is a 4:3 image and I thought that was not Where do you get the idea that a 720x480 image is 4:3? > > IF you have Wx480 being a 4:3 image then W can only be 704 for a SAR > of 10:11. Only way I see of getting 720 is to fudge things with the > assumption that 720x480 represents a 4:3 image OR use a SAR of 9:10. It much simpler than all that. 720x480 with a SAR of 10:11 isn't a 4:3 image. Just as 720x528 with a SAR of 1:1 isn't 4:3. There is no need to go to 9:10 land. > the 4:3 image - that's true for 10:11 but what about 9:10 which is > a number I've seen used. Wouldn't that make 720x534 -> 720x480 > the right thing to do? Either that or pad 704x480 to 720x480. IF the SAR was 9:10 for DV, the math is simple: 480 / (9/10) * (1/1) = 533.33 But it's not 9:10, it's 10:11. ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ Mjpeg-users mailing list Mjpeg-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mjpeg-users
